A large thorax is a sign of strong a diaphragm, substantial lung capacity, and serves as a solid foundation for the shoulders and arms.
Thoraxmaxxing seldom gets the attention it deserves in shaping a formidable and virile male physique. (foids appreciate girth.)
The thorax is meant to expand with the lungs as they fill with air. The more the ribs can expand, the more the lungs can as well. The limiting factor is generally the diaphragm.
If it’s weak then the thorax will have a difficult time reaching its potential.
A larger thorax is a dimorphic trait, we need to have larger lungs and have more cardio respiratory capacity.
This results in the typical male form characteristic.
Although much attention is paid to the shoulders, a large chest is what makes this possible.
These changes obviously take time but can be reinforced with targeted exercises for the diaphragm. Note that the ribs hinge upward during inhale. The sternum should be pushed out and upward as well.
One of the best exercises involves breathing against resistance (a light sandbag) while lying down. As you inhale, push against the weight with your sternum. Relax during the exhale.
Another exercise/cue is to elongate the entire spine by pushing your head up to the sky. This helps to prevent “shrinking” of the thorax, allowing the lungs to expand vertically.
As you begin to expand your lungs and thorax more and more, its default position and shape must adapt.
This should be part of your physique-building routine.
The benefits of a strong and healthy diaphragm are innumerable (that's why foids love it.)
@Whitepill @choripan @neymar @Harvey929